SHEAR VISCOSITIES OF CAO-AL2O3-SIO2 AND MGO-AL2O3-SIO2 LIQUIDS: IMPLICATIONS FOR THE STRUCTURAL ROLE OF ALUMINIUM AND THE DEGREE OF POLYMERISATION OF SYNTHETIC AND NATURAL ALUMINOSILICATE MELTS

Abstract

The shear viscosity of 66 liquids in the systems CaO-Al2O3-SiO2 (CAS) and MgO-Al2O3-SiO2 (MAS) have been measured in the ranges 1–104 Pa s and 108–1012 Pa s. Liquids belong to series, nominally at 50, 67, and 75 mol.% SiO2, with atomic M2+/(M2++2Al) typically in the range 0.60 to 0.40 for each isopleth. In the system CAS at 1600°C, viscosity passes through a maximum at all silica contents. The maxima are clearly centered in the peraluminous field, but the exact composition at which viscosity is a maximum is poorly defined. Similar features are observed at 900°C. In contrast, data for the system MAS at 1600°C show that viscosity decreases with decreasing Mg/(Mg + 2Al) at all silica contents, but that a maximum in viscosity must occur in the field where Mg/2Al >1. On the other hand, the viscosity at 850°C increases with decreasing Mg/(Mg + 2Al) and shows no sign of reaching a maximum, even for the most peraluminous composition studied. The data from both systems at 1600°C have been analysed assuming that shear viscosity is proportional to average bond strength and considering the equilibrium: